As a process of dewatering a substance containing moisture, a process using a chemical substance (working fluid) that changes in phase with changes in temperature and pressure is known. PTL 1 discloses as an example of processes for removing moisture from a high-moisture solid such as high-moisture coal, a dewatering process that uses a liquefied product of a substance that has high mutual meltability with water and exists as gas at the atmospheric pressure or a temperature near outside air temperatures, such as dimethyl ether.
PTL 1 discloses a configuration as follows. Dimethyl ether is pressurized and increased in pressure by a compressor to be made into gas of high pressure and high temperature. The gas is then cooled in a heat exchanger that performs heat exchange between a high pressure side and a low pressure side, to be converted into liquid of high pressure and low temperature. The liquid is then brought into contact with moisture in a moisture-containing solid in a dehydrator to dissolve the moisture, thereby dewatering the solid. The liquid is then decreased in pressure by an expansion mechanism to be converted into liquid of low pressure and low temperature. The liquid is then heated in a heat exchanger that performs heat exchange between a high pressure side and a low pressure side, to be converted into gas of low pressure and high temperature. The gas is then returned into the compressor.
The document states the following. With the above configuration, after the moisture in the solid substance is eluted in the liquefied dimethyl ether, while only dimethyl ether is selectively vaporized from the mixed liquid of the liquefied dimethyl ether and the moisture to separate the moisture, the moisture is simultaneously removed from the solid substance without being vaporized, and then the vaporized dimethyl ether is liquefied. Accordingly, dimethyl ether can be recycled.
On the other hand, since liquefied dimethyl ether is known to have a property of dissolving not only moisture but also oil, besides high-moisture coal, it is considered that the process can be applied to dewatering and deoiling of a substance containing moisture and oil.